1. Field of the Invention
This invention relates to a quick charge control apparatus and a control method thereof in order to charge a secondary battery such as a Ni-Cd (Nickel-Cadmium) battery or a Ni-MH (Nickel-MH, wherein MH is a metal hydride) battery.
2. Description of the Related Art
Generally, a constant current is used in quick charging the secondary battery. According to a conventional technique, as disclosed in Japanese Patent Publication Laid-open No. 103127/1990, a predetermined large amount of charging current is applied at an initial stage of a quick charge, and a full charge is recognized by detection of -.DELTA.V that is the detection of a drop in the terminal voltage of the battery from a peak value by a predetermined voltage of .DELTA.V. Upon detection of the fully charged state, the operation of quick charge is ceased.
In the conventional technique, a large amount of current is applied at the initial stage of the quick charge. Accordingly, quick recharge of the battery which has already been charged causes an upsurge in the temperature of the battery, thereby impairing the life of the battery.
In addition, because of the influence of the large amount of current as shown in FIG. 6A of the accompanying drawings, an overdischarged battery having a large portion of its capacitance discharged sometimes shows a voltage phenomenon similar to the voltage drop of -.DELTA.V which occurs when fully charged despite the fact that the battery has not yet been fully charged. For this reason, it was necessary to prohibit the detection of -.DELTA.V during a predetermined period, that is, between three and five minutes or thereabouts from the initiation of the quick charge. Therefore, as shown in FIG. 6B, if the quick recharge of the battery that has already been fully charged is effected, it was impossible to stop the quick recharge at least during the foregoing predetermined period independent of whether the battery is fully charged or not, thereby accelerating the deterioration in the life of the battery due to the uprise in the temperature.
Regarding the secondary battery, there are available several types of secondary battery such as a type A battery having charging characteristics wherein the battery shows a sharp decline in the terminal voltage at the end of the charge after having achieved a peak value and a type B battery having characteristics wherein there occurs an upsurge in the temperature of the battery.
As disclosed in Japanese Patent Applicatin Laid-open No. 190226/1990, a conventional battery charger is provided with -.DELTA.V charge control means for controlling a charge by the detection of the voltage drop (-.DELTA.V), and .DELTA.T charge control means for controlling the charge by the detection of uprise in the temperature (.DELTA.T). With the help of such means, the conventional battery charger can be applied to all types of batteries having different charging characteristics by selecting the control means dependent on the type of battery.
However, even in the case of secondary batteries having the same charging characteristics, each of the batteries may have a different value. For instance, although both the Nickel-Cadmium battery and the Nickel-MH battery have type A battery characteristics such that a gradual increase is brought about in the terminal voltage from the initiation of charge, and a sharp decline occurs after the terminal voltage has achieved the peak value, they are different from each other in the level of voltage drop .DELTA.V. Specifically, the level of voltage drop of the Ni-MH battery is smaller than that of the Ni-Cd battery.
Thus, the conventional technique is not fully applicable to the several types of batteries having similar charging characteristics, and consequently it was necessary to limit the battery to be installed in the conventional battery charger to only one type of battery.